Following U. S. President Dwight Eisenhower’s 1953 Atoms for Peace speech to the United Nations (Eisenhower, 1953), the U. S. and Russia exported research reactors to about 40 countries. At present, the IAEA lists 254 operational research reactors in 55 countries (Adelfang, 2011; see Figure 1-1). According to the IAEA, 75 civilian research reactors (excluding defense and icebreaker reactors) are currently operating using HEU fuel (see Figure 1-2). Nearly all HEU-fueled research reactors are supplied with HEU of U. S. or Russian origin, with the exception of a very few that are supplied with Chinese-origin HEU. About 25 percent of all research reactors are located in developing countries, including Bangladesh, Algeria, Colombia, Ghana, Jamaica, Libya, Thailand, and Vietnam.[12]

Civilian research reactors are used for a wide variety of missions, for example, to perform research in a broad range of scientific and engineer-

Planned 2

Under Construction
3

Total =

672 Research Reactors

ing disciplines, including research related to nuclear engineering, nuclear physics and chemistry, materials science, and biology. In addition, research reactors have become indispensible for the production of medical isotopes for diagnostic and therapeutic procedures and are also used for industrial purposes such as silicon doping.

Research reactors’ key missions require them to be designed differ­ently from commercial power reactors. Most notably, research reactors are typically designed to produce higher thermal neutron fluxes at much lower thermal outputs than power reactors. Most research reactors are also physi­cally much smaller than power reactors (typically having core volumes of less than a cubic meter versus tens of cubic meters) and require far less fuel (typically a few kilograms versus thousands of kilograms).

Research reactors have a broad range of designs in terms of power levels, moderators,11 fuel types, and cooling systems, among other design features. In many cases, these reactors are one-of-a-kind or few-of-a-kind, complicating efforts to convert them to LEU fuel. For illustrative purposes, one common broad category of research reactor—the pool — or tank-type water-moderated reactor—is described in the following paragraphs. A broad range of other designs exist, including fast research reactors, which require no moderator and use plutonium as fuel, and “homogeneous reac­tors,” in which the reactor core is a solution of dissolved uranium salts contained in a tank.

Pool-type or tank-type research reactors (see Figure 1-3) comprise a cluster of fuel assemblies and control rods[13] [14] in a pool or tank of water, which serves as both a moderator and a coolant.[15] The core is often sur­rounded by graphite, beryllium, or heavy water (the “reflector”) that is used to slow down (moderate) neutrons and reflect them into the core to maximize the neutron flux. The core and reflector typically contain empty channels for irradiation of targets and test materials, and some reactors are designed with apertures in their pool or tank walls through which neutron beams can be accessed. Figures showing the core configurations for a num­ber of different research reactors can be found in Chapters 2 and 3.

Fuel assemblies (also referred to as “fuel elements”) contain the ura­nium fuel that powers the reactor. A fuel assembly is comprised of indi­vidual fuel plates, tubes, or rods, the latter of which is also referred to as

“pins.” Each fuel plate or tube consists of the uranium fuel itself (the “fuel meat”) sealed in a “cladding” most typically constructed of aluminum. The number of fuel plates or tubes in an individual fuel assembly can vary widely. For example, a Russian MIR. M1 fuel assembly contains four tubes, whereas the outer fuel assembly of the U. S. High Flux Isotope Reactor contains 369 plates. An illustration of a Russian IRT-4M fuel assembly is shown in Figure 1-4.

Plate-type and TRIGA pin-type fuel is most commonly used in pool- and tank-type research reactors of U. S. origin, whereas tubular or pin-type fuel is used in Russian-origin reactors. Different fuel production methods— rolling in the United States and extrusion in Russia—are used as well.